Plasma Wave Spectrometer (PWS)

Description

The Plasma Wave Spectrometer (PWS) investigation had as its objectives to: (1) study plasma waves and radio emissions in the Jovian magnetosphere; (2) investigate the role played by these phenomena in controlling the scattering and/or loss of trapped radiation; and, (3) derive fundamental plasma parameters (e.g., electron density) from the observations.

The PWS instrument consisted of one 6.6 m tip-to-tip electric dipole antenna (mounted on the end of the 10.6 m magnetometer boom) and two search coil magnetic antennas (mounted on the high-gain antenna feed). The dipole antenna was composed of two elements mounted in opposing directions perpendicular to the magnetometer boom as well as to the spacecraft spin axis. Each element was hinged 1.8 m from the tip to permit folding during launch.

The dipole antenna measured electrostatic waves in the frequency range 5.62 Hz-5.65 MHz. One of the search coil magnetic antennas was optimized for low frequencies (5 Hz-3.5 kHz) and the other for high frequencies (1-50 kHz). The high-frequency antenna was oriented perpendicular to the electric dipole antenna while the low-frequency sensor was oriented parallel to the electric dipole antenna.

Signal processing for the PWS was performed in a single electronics package. Two main systems, a low-rate one for survey spectra and a high-rate one for high-resolution spectra, processed the incoming data. The low-rate system consisted in turn of three spectrum analyzers: high-, low-, and medium-frequency. The high-frequency spectrum analyzer provided 42 frequencies between 100.8 kHz-5.645 MHz with a fractional spacing of 10.0% and a bandwidth of 1.34 kHz. The medium-frequency analyzer provided 112 frequencies from 40 Hz-160 kHz with a fractional spacing of 8.0%. The frequencies of this analyzer were divided in four bands of 28 frequencies. The bandwidths associated with these bands (in increasing frequency order) were 4.26, 6.67, 120, and 1510 Hz. The low-frequency analyzer provided four logarithmically-spaced channels between 5.62-31.1 Hz with bandwidths of 0.83, 1.86, 2.75, and 4.79 Hz and a fractional spacing of 67%. A complete spectral sweep required 18.67 s for all three analyzers.